Fig. 1.

Conceptual models illustrating current and emerging frameworks of soil bioavailable N cycling. The emerging model emphasizes three major compartments: (1) depolymerization and solubilization, in grey; (2) interactions between bioavailable organic N and minerals, in orange, and (3) microbial assimilation, recycling, and mineralization of organic N, in blue. Black arrows represent the direction of N flow between pools. Green arrows indicate the direction of plant root exudate C flow. This model does not attempt to capture all steps in the process (see Future Directions). The "current view" is

adapted from Schimel and Bennett 2004. (Color figure online)